Journal of Avian Biology最新文献

Age is an important trait, influencing an individual's physiology, behavior, and survival probability. Unfortunately, the ages of wild animals are often unknown, impeding behavioral and ecological studies requiring life history information and impacting conservation efforts for threatened species. Epigenetic clocks offer a solution by generating accurate age estimates based on DNA methylation at particular CpG sites, which changes in a predictable manner over lifespan. The CpG sites correlating with age vary across species, requiring species-specific epigenetic clock calibration using DNA methylation measured at CpG sites across the genome. Here, we compared the efficacy of two DNA methylation sequencing methods, whole genome enzymatic methyl sequencing (WGEM-seq) and epiRADseq, in calibrating epigenetic clocks for chestnut-crowned babbler Pomatostomus ruficeps nestlings (n = 56, aged 0–19 days). We found that epigenetic clocks using WGEM-seq data outperformed clocks using epiRADseq data (MAE = 1.6 versus MAE = 5.9; r = 0.95 versus r = 0.41 for 10-fold cross-validation). Notably, WGEM-seq achieved superior performance despite utilizing fewer loci in the input data than epiRADseq, indicating that the lower resolution of epiRADseq does not allow for accurate clock calibration. Using WGEM-seq data collected throughout a small fraction of the lifespan of chestnut-crowned babblers, we successfully calibrated a highly accurate epigenetic clock. These results open promising avenues for investigating the impact of early life environments and developmental stressors on aging. The insights gained from such studies can improve conservation and management strategies while deepening our understanding of avian life history strategies, ecology, and behavior.

Rising global temperatures will have profound impacts on species and ecosystem functioning. Species existing near their thermal thresholds will be particularly vulnerable to these changes, and those species that rely on, or preferentially use, artificial structures may face pronounced effects. Gaining insights into the anticipated climate changes, both present and future, is crucial for informing conservation practices and the utilisation of artificial structures in conservation efforts. Using three years of data, we quantified and compared temperature of artificial nest boxes installed between 1986 and 2006 and natural nest burrows of a fringing population of little penguins existing at the northwestern limit of their range. Nest boxes were ineffective at replicating conditions of natural nests, exhibiting consistently higher daily maximum temperature (~ 2˚C) and exceeded upper thermoneutral limits for longer than natural nests. Fine scale biotic and abiotic nest characteristics influenced maximum nest temperature and time exposed to temperatures ≥ 35˚C. Simulated temperature increase of 2˚C predicted an increase in the number of days exceeding thermally stressful conditions (≥ 35°C) by up to 49%. Such increases will expose penguins to potentially fatal thermal conditions, particularly during the late breeding and moulting phases of their annual cycle. This study revealed that current and future thermal environments of little penguin terrestrial habitat on Penguin Island can exceed physiological limits for this species. Intervention to improve artificial nests and better quantify consequences is urgently needed given recent estimates of a declining population and increasing risk of local extinction.

Human-induced alterations in natural water flow have seriously impaired the integrity of riverine ecosystems. Nonetheless, even in human-altered riverine and adjacent terrestrial habitats, there is considerable potential for the protection of rare species if management practices prioritize biodiversity conservation. However, the management of such areas often presents complex challenges. On the one hand, efforts to mitigate natural hazards frequently overshadow biodiversity conservation objectives. On the other hand, high-resolution maps of forest structures are often lacking but could be very useful for spatial prioritization of conservation efforts, especially as vegetation structure can be directly managed through local restoration activities. Here, we used an airborne LiDAR-derived vegetation structure along an 80 km stretch of the Rhône River (Valais, Switzerland) to assess the habitat characteristics that best explain the presence of a flagship species, the common nightingale Luscinia megarhynchos, a species that historically thrived along this river system but has experienced a drastic population decline over the past decades. Nightingales showed a preference for dense vegetation in the lower strata above ground (3–6 m), as opposed to an open and sparsely vegetated ground level (0–1 m). The preferred habitats were predominantly located within forested regions, as indicated by a preference for taller canopies. These findings align surprisingly well with prior field research on the species, demonstrating the capability of high-resolution LiDAR to upscale locally derived habitat preferences across very large areas. Based on LiDAR outputs, we proposed management recommendations for the whole river. Such spatially detailed information furthers our understanding of local habitat preferences of endangered species, thus facilitating the formulation of conservation recommendations at the scale of entire populations.

When individuals of the same population do not respond uniformly to the same situation, they might experience divergent fitness outcomes, such as different survival rates when facing danger. When these behavioural differences between individuals are consistent across time and contexts, they are referred to as ‘animal personality'. We here explored the response to a risky situation as a potential personality trait in free-ranging common ravens Corvus corax. We experimentally tested the repeatability of behavioural variables along the boldness–shyness axis of 12 individually marked ravens belonging to a large non-breeder population in the northern Alps. We played different audio cues of natural (i.e. calls of birds of prey) and human-induced (i.e. gunshots) threats during a predictable feeding situation and scored startle reactions of individual ravens. Results revealed age-specific differences in behavioural responses, but no consistency across time. Young ravens had shorter latencies to feed after our playback stimuli and all ravens reacted with more anti-predator behaviour towards birds of prey calls than gunshots. The missing affirmation of repeatability along the boldness–shyness axis is partly in line with previous findings on the exploration axis in captive ravens, and fits with the reports of high behavioural flexibility in this species. Nevertheless, it is conceivable that our present methodology for assessing boldness–shyness does not fully align with the situational strength and relevance required for foraging ravens, and/or that consistent inter-individual differences become pronounced at specific life stages (i.e. during breeding).

Obligate avian brood parasites lay their eggs in other bird species' nests, leaving these hosts to rear the parasitic young. To eliminate or reduce the costs of parasitism, many hosts have evolved the ability to recognize and reject parasitic eggs, and most use eggshell color for recognition; however, color discrimination should be more challenging in the low-light conditions facing cavity-nesting hosts. Therefore, we hypothesized that instead of color, cavity-nesting birds could rely on perceived differences in brightness (i.e. luminance) and on light levels in their nests for egg recognition. Specifically, we expected that rejection rates would be higher when foreign eggs are lighter or darker than the hosts' own eggs or when nest light levels are higher. To investigate this hypothesis, we experimentally altered the luminance of 413 similarly colored (blue) experimental model eggs and added these experimental eggs to the nests of cavity-nesting eastern bluebirds Sialia sialis that typically lay immaculate blue eggs. Contrary to our expectations, neither the perceived luminance of the eggs nor the amount of light in the nest cavity predicted host responses. Therefore, it is unlikely that bluebirds base their antiparasitic decisions on perceived differences in eggshell luminance. Our work provides a foundation for future studies that can inform us about how cavity-nesting birds perceive salient visual stimuli in the dim light conditions of their nests.

Wading birds have declined globally, with particularly pronounced declines in western Europe. Multiple species are now on the IUCN Red List, with northern lapwing Vanellus vanellus near-threatened and declining. Historically, habitat degradation, including that from wetland drainage and agricultural intensification, has contributed to population declines. More recently, declines have been attributed to poor breeding success due to unsustainably high rates of predation on eggs and chicks by avian and mammalian predators. In the UK, the red fox Vulpes vulpes is a major mammalian predator of waders. However, the Eurasian badger Meles meles has increased in range and abundance, and can occur at high densities, with potential for acute localised predation impacts on vulnerable wader populations. Factors affecting rates of badger predation on wader nests remain unexplored. We investigated what these factors might be, analysing data from six years of lapwing nest monitoring at a breeding site in northeast Scotland. A negative impact of temperature was detected, where the overall probability of badger predation was above 0.1 when the mean daily temperature was below 4°C during the preceding 7 days, dropping close to zero when above 10°C. Badger predation on lapwing clutches also increased with earthworm availability, and inter-annual effects were observed matching variations in temperature, whereby intense badger predation in 2021 coincided with unseasonably cold temperatures and low lapwing breeding productivity. This highlights the potential for weather forecasting to be used to deploy pre-emptive non-lethal management strategies to mitigate badger predation impacts on lapwing nests.

Based on the concept of the extended phenotype, bird nest characteristics can serve as indicators for adaptations to changing environmental conditions. We examined how the nest mass of three cavity-nesting tit species (Paridae) varied across 22 mixed forests in Germany in response to elevation, canopy openness, and species body mass. We predicted that nest mass should increase with elevation and canopy openness, due to thermoregulation being more demanding in colder or warmer climatic conditions, and decrease with body mass, as larger species have greater thermoregulatory capabilities. To test these predictions and to assess the consequences of nest mass variation for reproductive success, we recorded nest mass, clutch size, and pre-fledging brood size in 576 standardized nest boxes. Nest boxes were installed along an elevational gradient of approximately 1000 m a.s.l., either in forest gaps with fluctuating microclimatic conditions or in closed forests with buffered microclimates. We found that nest mass increased by ~ 60% along the elevational gradient, but the effect of canopy openness on nest mass was not significant, while nest mass decreased along the ranked species from the smallest Periparus ater to the medium-sized Cyanistes caeruleus and the largest Parus major. Structural equation modeling revealed that heavier nests were associated with larger clutch sizes, which in turn resulted in larger pre-fledging brood sizes. Altogether, our results suggest that forest tits adjust nest construction in response to macroclimatic conditions, thereby compensating for the thermoregulatory challenges posed at higher elevations and their small body size. This strategy may be critical for maintaining reproductive success in changing environments.

Studies on bird behavior have benefited from the miniaturization of tracking devices and the opportunities for massive data collection facilitated by extensive satellite and cellular infrastructures. However, assessments of the effects of tracking devices on the behavior and survival of birds are rarely conducted and disseminated – raising animal welfare concerns, risking project failure, and hindering optimization of tracking methods within the ornithological community. We quantified the effects of tracking devices on banded dotterels Anarhynchus bicinctus – a threatened, small-bodied (median 59 g), partially migratory shorebird native to New Zealand and a priority for conservation planning on Austral flyways. We deployed ten 1.2-g archival GPS loggers and ten 1.8- to 2-g Argos satellite transmitters on breeding dotterels in Kaikōura, New Zealand. Including leg rings and silicone-tubing leg-loop harness, deployments constituted 2.7–4.3% of an average individual's mass (or 1.9–3.4% for the device alone). Both tracking devices documented the curiously mixed winter strategies characteristic of banded dotterels: migrants flew north to the upper North Island or south to the Canterbury Plains, while other individuals stayed resident in Kaikōura. Compared to a control group of 74 dotterels without tracking devices, neither technology had adverse effects on subsequent breeding outcomes, annual apparent survival, behavior, or body condition, but Argos satellite trackers provided data over a longer period than archival GPS loggers. One possible reason for the absence of adverse effects could be that banded dotterels (and other Charadriinae species) primarily rely on ground-based locomotion, characterized mainly by walking and running – movements that are less hindered by the added mass of auxiliary attachments. Our findings support the ‘3% rule' (i.e. using device weight alone as a guideline), but we suggest that deployment limits of tracking devices could be refined by considering both the species' ability to carry additional weight and its primary mode of locomotion.

Feathers are critical for locomotion, communication, thermoregulation, waterproofing, and protection from UV radiation. To maintain these functions, birds care for their feathers by grooming, which consists of preening with the bill and scratching with the feet. Grooming cleans and arranges feathers, distributes preen oil and powder down, and removes ectoparasites. Birds devote considerable time and energy to grooming, to the exclusion of other activities, such as foraging. All else being equal, birds should aim to minimize their grooming time. Seasonal changes in grooming have been documented, with some species of birds grooming more in summer than winter. The higher rate of summer grooming may be caused by molt; however, the relationship between the dynamics of grooming and molt have been quantified only in captive birds subject to other manipulation, such as induced molt in poultry, or access to mates in zebra finches. We conducted an eight-month study of wild-caught feral rock pigeons Columba livia to compare rates of grooming and molt. We found that the intensity of grooming parallels the intensity of molt throughout the molt cycle. Pigeons more than double their grooming time at peak molt, consistent with patterns observed in wild birds. Our results suggest that molt may be more energetically costly than previously realized, given concomitant increases in grooming.